Many methods and products have been developed, for example, to deter counterfeiting of valuable documents including art work, identification documents or financial instruments such as currency, so that unauthorized copies attempted to be made from those documents can be readily distinguished from the originals. Most of these methods and products involve preparing an original document by printing or lithography on high quality media such as silk, rice paper, and high contact rag paper. The printing of original documents may be done either in black-and-white (B&W) or in color, and if in color, either in spot color, colored backgrounds and/or multicolor printing. In the case of color, the tendency has been in the direction of using multiple colors for original documents for aesthetic value, for ease of recognition, and originally for protection from copying by conventional means. The common printing processes of valuable originals, whether in B&W or in color, are intaglio and gravure, among others. These and the other processes mentioned in this application are very well known in the art and will not be discussed in great detail.
Most of the useful examples in the prior art to deter counterfeiting and the like are intended to ensure that copies are produced either with a clear moiré pattern or with a “latent image” indicia which is invisible or nearly invisible to the naked eye on the original document. The term “latent image” is used here not in the photographic sense of an unseen image to be developed after processing by chemical reaction, but to indicate indicia that are printed on originals so as to be nearly invisible to the naked eye.
These and other developments in the prior art for purposes of providing document protection are disclosed in the patent literature, as for example, in U.S. Pat. No. 5,018,767 issued May 28, 1991; U.S. Pat. No. 5,193,853 issued Mar. 16, 1993; and U.S. Pat. No. 3,675,948 issued Jul. 11, 1972; and U.S. Pat. No. 4,143,967 issued Mar. 13, 1979, all to Ralph C. Wicker; in U.S. Pat. No. 4,227,720 issued Oct. 14, 1980 and U.S. Pat. No. 4,310,180 issued Jan. 12, 1982 both to William H. Mowry, et al, as well as U.S. Pat. No. 5,149,140 issued Sep. 22, 1992 to Mowry et al; and in U.S. Pat. No. 5,487,567 issued Jan. 30, 1996 to John R. Volpe. All of these patents disclose various means for providing methods and products to enable copies of documents to be distinguished from the originals, as for example, by a “large dot-small dot pattern”, a “close line-spaced pattern”, and images or indicia which are screen printed at minutely varied spaces and/or angles on the originals and are intended to produce a highly visible moiré pattern effect on the unauthorized copies. In this specification, the words “print”, “printed” and “printing” are used to refer to the making of an original document regardless of the techniques used, and the words “copy” and “copying” to refer to making copies from an original.
It is well known, however, that copier and computer scanner-printer technology has become even more sophisticated since the development of the prior art in document protection. The goal of copier technology, if not already achieved, has been, especially in desktop publishing and the like, to obtain copies as good as an original. “What you see is what you get” in color documents has become very achievable in copier and duplicator equipment including scanning input devices. Even desk-top computers have become sufficiently sophisticated in color reproduction, including color matching of copies to color standards such as the PANTONE.RTM. Color Matching System.
Many if not all of the document protection methods and products were developed before this very significant improvement in copier and computer reproduction technology, and have been found not be as effective in the newer color reproduction technology. This is especially the case on color copiers with a “photo” setting that intentionally copies a document in an “unsharp” focus so as to give the effect of a continuous tone image, the effect of which is to defeat the precise line variation between the copier scanner and the security pattern on the document original. These prior art techniques for document protection may not work as reliably against the many forms of copier/duplicator and computer scanner/output equipment now or soon to be available.
Thus it has become imperative for purposes of document security and safety that further improvements in the area of document protection be found, especially where there is a need to prevent copying or duplicating of valuable originals and readily distinguishing the copies from the originals.